1. Field of the Invention
The present invention relates to a rapid response h-q-T sensor. More particularly, two sensors are designed to simultaneously measure heat flux (q) and surface temperature (T) on parallel paths, thereby generating data that enables calculation of the heat transfer coefficient (h) and recovery temperature (Tr). Most particularly, the present invention uses thin film sensor technology to measure the upper-bound, i.e., uncooled boundary layer, stagnation-point heat transfer condition.
2. Brief Description of the Related Art
Thin film heat flux and temperature sensors have been developed by Vatell Inc. of Christiansburg, Vir. See U.S. Pat. No. 4,779,994, issued to Diller et al. Such sensors include a rapid response device suited to capture rocket plume conditions such as the HFM-1 (Heat Flux Microsensor), described in High Temperature Heat Flux Measurements, by J. M. Hager and L. W. Langley of Vatell Corporation of Christiansburg, Vir., and S. Onishi and T. E. Diller at the 29th Aerospace Sciences Meeting, Jan. 7-10, 1991 in Reno, Nev. The HFM-1 measures heat flux (q) and wall surface temperature (Twall), producing a voltage out of the sensor thermopile array that is proportional to heat flux (q), with the voltage having a polarity indicating the direction of the heat flow. However, the HFM-1 design lacks the ability to establish values for the heat transfer coefficient (h) and the recovery temperature (Tr) that are useful in modeling severe thermal (e.g., rocket plume) environments.
Several patents have disclosed many aspects of sensor thin film technology, including U.S. Pat. No. 4,779,994 (Diller et al.), U.S. Pat. No. 5,379,718 (Onishi), U.S. Pat. No. 5,765,075 (Yamamoto), and U.S. Pat. No. 5,798,684 (Endo et al.), the disclosures of which are herein incorporated by reference. However, these patents do not address the methods of measurement and the means of calculation of the heat transfer coefficient (h) and the recovery temperature (Tr) as taught by the present invention.
The heat transfer coefficient (h) is a widely used parameter that provides a measure of combined radiation, convection, and conduction heat transfer modes for the thermal energy generated from a source of heat energy. The recovery temperature (Tr) provides a measure of peak temperature in a flowing mass efflux and offers a means to characterize the total energy within the flow stream. This is particularly important to know for supersonic applications in which aerodynamic heating becomes an important design driver.
It is an object of the present invention to provide a thin film sensor assembly that has a fast response and is thereby usable in severe thermal environments.
It is further an object of the present invention to provide a thin film sensor assembly that provides the data necessary to determine the heat transfer coefficient (h) and the recovery temperature (Tr) condition at a point in the measured mass efflux.
These and other objects are accomplished by the present invention which includes a thin film sensor comprising at least a first thin film, a first thin film heat flux indicator and temperature indicator integral to the first thin film structure mounted on a first substrate and capable of indicating a first temperature and a first heat flux into the front surface, and a second temperature sensor. Preferably, the second temperature sensor provides a temperature measurement at a different point on the front surface of the first thin film on the first substrate. In an alternative embodiment, the second temperature sensor may be integral to a second thin film assembly mounted on a second substrate electrically and thermally isolated from the first thin film assembly. In either embodiment, the thermal resistance between the second temperature sensor and a reference is much greater than that of the thermal resistance between the first temperature sensor and a reference. The present invention further includes a method for determining a heat transfer coefficient, h, comprising the steps of providing a thin film sensor assembly comprising at least a first thin film, a first thin film heat flux indicator and temperature indicator integral to the first thin film structure mounted on a first substrate for indicating a temperature and a heat flux into the front surface, and, a second thin film temperature indicator that provides a temperature measurement at a different point on the front surface of the first thin film on the first substrate in which the thermal resistance between the second temperature sensor and a reference is much less than that of the thermal resistance between the first temperature indicator, the first heat flux indicator, and a reference then, the h-q-T sensor assembly 10 is exposed to a severe environment.